1 Field of the Invention
This invention relates to apparatus for logging wells during drilling and to methods for making such apparatus.
2 The Prior Art
Although the advantages of simultaneously drilling and logging a borehole have long been recognized, such services have developed slowly because of the lack of reliable equipment which can be quickly repaired or replaced in the field.
Many prior art patents disclose various types of electrically insulated sleeves fitted around the drill string with instrumentation just above the drill bit in an attempt to measure while drilling such variables as formation electrical resistivity, self-potential, temperature, pressure, radioactivity, directional deviation of a drill hole, and the like. Examples of such apparatus are shown in U.S. Pat. No. 2,568,241 to Martin, U.S. Pat. No. 2,930,137 to Arps, U.S. Pat. No. 3,149,683 to Clements et al, and U.S. Pat. No. 3,293,542 to Piety.
The disadvantage of the sleeves previously proposed for logging while drilling is that they often cannot withstand the severe abrasion and shock encountered downhole while drilling, and cannot be readily removed and replaced in the field, which severely limits their utility. Copending application Ser. No. 141,769, filed Apr. 21, 1980, discloses an improved sleeve for logging-while-drilling, and methods for making the sleeve. This invention provides further improvements in the sleeve and methods disclosed in copending application Ser. No. 141,769.